How to modify single key value pair with Charles proxy rewrite - regex

Question

I would like to modify the value of a single key in a larger json response body using Charles proxy re-write.
As an example, I want to change age from 20 to 30 (but can be any initial value):
{
"userId": "some_value_i_dont_want_to_touch",
"username": "Charlie",
"age": "20"
}
I do not wish to replace the entire json body as that is not practical for my situation; I just want to modify the value of a single key.
The regex "age":[\s\S]"(.*)" or "age":[\s\S]"[^"]+" highlights the text I want on sites like https://regex101.com/
I've tried a few variants of this as well, but none of them seem to actually change the value.
Example screenshot
If I just enter the Match value "20" and the Replace value as "30" it works which tells me I have the url and path correct, but I'd like to avoid accidentally replacing the wrong thing.
Using the current full value without regex doesn't work either, so trying to do "age": "20" -> "age": "30" doesn't work, but maybe I need to escape something, though this would also limit me to cases where I know the value beforehand which is not ideal.
The error logs also indicate the request was re-written, but nothing changes
Ex: Running: Body: "age":[\s\S]"(.*)" -> "age": "30"
I am not clear on how the groups work (with the $) but maybe this has something to do with it.
I am probably just missing something obvious or going about this wrong.
Any insight would be appreciated.

Answer 1

For this topic, perhaps there is no whitespace needed because a proxy response is a text string with no spaces, however when we view it in JSON Text it helps us to read(thus having white spaces)
For the rest like me who is new that may help!
I just learnt that for [ needs to be escaped for regex to work, etc:
Match:
"xxxx":\[] #tick regex
or you may,
^"xxxx.{0,}"
xxxx refering to anything that starts with (^)
" at the end marks the end of the string or else it'll match everything else
Replace:
"xxxx":\["new"]
Hope this helps!